The compatibility tests did not make it out of the annealer...except for a couple and they blew apart right at the saw. First pic has some all-brossphate pieces to show the color at the top. At the bottom, the broken pieces are inside or outside color-clear...no difference. Last 2 pics show the color intensity achieved for a couple all brossphate pieces.

I've got my work cut out but I'm hoping for a little direction. My only clue is the E&T measurement which for Dave's 2.5% is only 92.6 while Pete's silver opal is 94.1. The silver opal has fit perfectly for me to Cristalica with ring tests for final proof. I have no idea what the Cristalica E&T would be so I have to make a guess that it's closer to Pete's than the Brossphate.

I'd like to intensify the phosphate similar to Jordan's results. Coincidentally, I can raise the E&T to 95.1 by increasing the phosphate 3.6%, but is this really a good way to modify the expansion? Pete usually points to soda ash and sand for moving the expansion. Should I use soda/sand to find a compatible 2.5% glass or just modify the phosphate and see if I can kill 2 birds with 1 stone?

Thanks for any input and to Dave for sharing this formula. My results need work but that was really fun to work with!

Using Dave's calculator I would shoot for 91 LEC for something compatible with Cristalica. My notes indicate the more phosphate you add the lower your target number will be. I melted a 5% that showed 1 point high in a trident seal but no stress showed in the product under the polarimeter. The calculator shows a theoretical 87.75 LEC. Melting a phosphate opal will yield different results than a straight soda lime calcedonia. You can really only rely on your previous phosphate tests as a guide.

Wow...thanks Jordan! I had a hunch that making LEC adjustments with the phosphate was a bad idea. I am awaiting a package of a la carte ingredients from Jim at East Bay including his sand. I'll be able to tune this in a bit on my next batch.

I'd be interested to know if you got the fit worked out for the 5% with 1/2 borax and if it needs 2300 to melt.

I considered the 5% recipe compatible due to the product showing no stress. I melted at 2300 and I would recommend higher if possible. Go ahead and make LEC adjustments, just don't rely on your non phosphate batches as a guide.

I'm really only interested in doing this at lower temps...2200 max. It melted fine with the full amount of borax so I'll work with that. It did seem to have a sweet spot in the pot so I'll have to work on stirring more.

Good points. I used 20 mule borax from the store which is 10M. I performed a molar equivalent calculation to determine the correct amount to add. Derived this little chart for my own quick calculations.

Borax equivalents
5M lb 10M lb
1 1.31
5.2 6.80
9 11.77

Jim doesn't carry lime hydrate and instead used a high purity whitening. I took a cue from your conversion of the unoxidized formula going from lime hydrate to whitening and again performed a molar conversion on the calcium content.

Calcium equivalents
Whitening lb Lime lb
1.35 1
7.42 5.5

The formula doesn't have feldspar...just alumina hydrate.

One of these changes may have caused issues. I worry about the use of whitening but as you were exchanging it in the unoxidized I really wasn't concerned about it. Jordan's point about all rules being off on this type of glass has me questioning everything.

It's called "Whiting" and that's yet another name for Calcium Carbonate, also called Marble Dust, Lime, and a few others but it's all CaCO3. Hydrate is CaOH. Big differences on that Borax as well. Most formulas call for 5 mole, not ten. There is also anhydrous borax.

In some spreadsheets, it may not let you try both so the thing to do is to zero everything in the spreadsheet and then just add the single item, like feldspar. Then look at how your spreadsheet( that you likely didn't write) assigns the components for feldspar. Some will now be silica, some alumina but then it gets interesting where it puts sodium and potassium and in some cases (spodumene) lithium. The same sort of thing will happen with Borax, or alumina, so pay attention. The differences between Hydrated alumina and calcined are large.
After that, you may develop interest in how much moisture you are carrying around in a bag on chemicals that is additive and not chemically bound. If you had 1% moisture in a 100 lb bag, it's got 1 pound of water in it. Continue pondering that math when you look at expansion factors. Fritz used a simple trick to determine moisture. He put 100 grams of the questionable material in an annealer and turned it up to 250F for four hours. Then he measured the weight a second time. If it now weighed 97 grams, it was 3% water.

Doing this successfully requires a lot of careful deliberation and some occasional navel gazing.

That's a much better way to put it. However, when you're trying to match a clear as I am it seems like the rules have to be bent a bit. Your observation that a LEC of 91 is needed for a 2.5% phosphate and 87 is needed for a 5% is showing a trend where the spreadsheet says one thing and the glass does another. My results seem consistent with yours in that the original formula at 94.1 is not compatible with Cristalica. We'll see if a straight-forward drop of LEC to 91 makes all the difference.

Both Pete and Dave make their own clear and colors. They found their clears to be compatible with the straight Brossphate formula. Could be that their clear formulas are a better match to Brossphate. Pete's is much different from Cristalica as he has described. There is more than COE to compatibility as your results make clear. That their clears are also compatible with 96 colors would seem to make them a better choice. Who knows how the Brossphate (@91 LEC) is going to react to a 96 COE color when the LEC is pushed down just to fit the Cristalica.

Don't over think it. Just work with what you have. Make a change, observe the result, make another change, rinse and repeat. The only thing that is really a constant is the clear you are using. Make it compatible with your clear and you shouldn't have a problem with *most* colors out there. If you do, chances are that other color may have been a little on the fringes of compatibility as well.

Might sound stupid but I wish I could be there to help. I'd enjoy seeing someone else's approach to element furnace building. I just do my best without a whole lot of knowledge or experience. I'm a good weldor/fabricator but that's just a small part of the success of a build.

Don't worry, I'm not trying to invite myself...I work this weekend

Pete, thanks for the advice on keeping things linear. I'm completely isolated from other glassblowers here in Bozeman and sometimes just go off on tangents to discuss glass with you folks. It's tough to just be your own sounding board all the time.

What really matters most is that the glasses match expansion at the point where they set up...usually referred to as softening or strain point. This gets tricky with time and temp but fortunately you can overcome much of the trickery by moving the expansion of one of the glasses.

Quite often two matching glasses will have very different calculated expansions.

Think of the calculated expansion as a number you use to see where you're going as you experiment to make two glasses match.

Linear expansion Coefficient L.E.C describes the linear expansion of a glass, nominally in a 4.000 length approx 4mm in diameter heated from 19C to 300C.
That's where your number comes from.

Coefficient of expansion doesn't even say what kind of expansion. C.O.E. I believe was an expression Theresa at C&R Loo used way the hell back when, and she was trying to get some useful information out there about what might fit what when information was in short supply. It does not mean anything however, thus my objection. Lani MacGregor queried about this and you can find the thread on that in Antiques and Classics.

Since varying thermal guides have been used in various tests, the temperature range has varied. Some systems tested from 19C to 300C, some tested from 200C to 400C. There's a lot of odd stuff but it becomes apples and oranges. So you get to where SP87 is actually a 96... E &T never tested colorants at all. Winkleman and Schott did do an enamel study back around 1925 for that industry on many metallic oxides but the temp ranges were not comparable. A major mistake was made in 1975 or so when Paul Manners put together an article for Glass Magazine called "Custom Made to Fit" which was a very helpful application of Algebra to the issue. There was however a fatal flaw and Paul co-mingled the different studies into one chart. Then Henry Halem canonized that mistake by including it in Glassnotes 3. Fortunately Henry removed that at my urging before Glassnotes 4 was taken to print. Appen does have a far more complete set of factors but it does assume you will calculate your glass using mole chemistry to really be accurate.

With the guidance from Jordan that his 5% is a theoretical 87.8 LEC to match Cristalica, I made a 3.2% with a 90.2 LEC. Wanted to try a bit more phosphate for the white I want to achieve.

Good news: I love this glass! The color was amazing and came on easily after just a couple strikes. Melted well even with more silica...lots of stirring and kept my borax level the same. I'm doing an overnight at 2180 after melting it all down at 2112. Both the Brossphate and my chalcedony really like this high temp period to get everything melted in.

Bad News: Made it out of the annealer, but...no rings for a test. I sawed another cylinder of known compatible glasses and that was fine. I'm going to try and get closer to Jordan's 5% LEC number next time.

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